In the past, protective helmets for cyclists have been manufactured according to the configuration and structure of motorcycle helmets, which can be defined as, a hard shell type. More recently, based upon helmet users' requirements for a lightweight cycling helmet, manufacturers have used only a thick foam material. Although the foam only helmets usually provide protection, they have limited durability because the plastic foam material is easily damaged due to abrasion, bumps, scratches, and physical deterioration.
One remedy adopted to improve the durability of the plastic foam helmet has been the use of helmet covers made of fabric which, in addition to preventing damage from abrasion and scratches, also provides a decorative function. Another remedy adopted has been to include a thin outer hard plastic microshell having less thickness and weight than the traditional hard shell type helmet, but having better resistance to damage and greater durability than the fabric covered helmet, over a relatively thicker inner foam plastic shell.
Thus, based on the above description, the following general categories may be defined for protective helmets used by cyclists:
(a) hard shell helmets having an outer shell, normally made of a thermoplastic material such as: NYLON, polycarbonate, or ABS with a thickness varying from 2 to 3 millimeters, an inner shell made of a deformable foam plastic such as expanded polystyrene styrofoam (EPS), a comfort liner inside the EPS foam shell, and a retention strap system attached directly to the outer hard shell;
(b) foam helmets having a relatively thick outer shell made of EPS, a comfort liner, and a retention system attached directly to the outer foam shell; and
(c) microshell helmets having a thin outer microshell (0.2-0.5 millimeters thick) made of a thermoplastic vacuum-shaped material such as polyethylene or polyester over a relatively thicker inner plastic EPS foam shell and a comfort liner. Due to the thinner nature of the outer microshell, the retention strap system is attached to the EPS foam shell.
These known helmet constructions exhibit different degrees of protection for a wearer during crash impacts. The hard shell helmet absorbs part of the impact energy by deformation of the outer shell. The outer shell also distributes the impact energy to the inner EPS shell over a contact area larger than the impact area of the outer shell, and the remaining impact energy is absorbed by the deformation crush of the inner foam shell. Impacts on the hard shell helmet do not affect the retention strap system, because it is attached directly to the outer shell.
In a similar crash impact situation for the foam only helmet as well as for the microshell helmet, all the impact energy absorption work is provided by the EPS foam shell by direct deformation. However, this implies some negative consequences because the energy of impact is concentrated at a single point having the same area and dimensions as the impact-causing body or structure. Consequently, a thicker EPS foam shell is required to provide the same energy absorption capacity as the hard shell helmet. Also, for impacts occurring close to the lower edge of the foam helmet, and especially in proximity to the vent openings, cracking of the EPS foam shell becomes almost inevitable due to the wedging effect of the impact-causing body against the helmet. In some cases, a crash impact may cause the helmet to crack and break into multiple pieces, thereby destroying its usefulness.
If the foam helmet is submerged in water, as is required by most international standards and test procedures, the foam shell absorbs some quantity of water. The absorbed water penetrates the interstices between the plastic foam particles or spheres and, when compressed, the crash energy tends to separate the adjacent spheres thereby worsening the cracking phenomena described above. A cracked shell has a reduced energy absorption capacity, which in most cases is much lower than that required to meet the international safety standards. Moreover, a cracked helmet shell would completely void the function of the retention strap system. Finally, it is important to note that a cracked foam shell would not provide any useful protection to a wearer in the case of multiple impacts immediately occurring, one after the other, in an accident or crash.
Thus, it is apparent that an improved construction for protective helmets for cyclists is needed. The known prior art has provided various designs of protective helmets which are useful, such as disclosed by U.S. Pat. No. 4,443,891 to Blomgren et al., U.S. Pat. No. 4,472,472 to Schultz, U.S. Pat. No. 4,558,470 to Mitchell et al., U.S. Pat No. 4,612,675 and U.S. Pat. No. 4,653,123 to Broersma, and U.S. Pat. No. 4,845,786 to Chiarella. However, these helmets generally utilize bondable plastic members or unreinforced resilient padding to provide a shock absorption function. Thus, the prior art helmets do not provide proper combinations of light weight, high impact energy absorption and multiple impact protection, and ventilation which is desired by the helmet wearer.